Research Article
Survey on Different Routing and Wavelength Assignment
Techniques in WDM Optical Networks
Shashma. M, 1 Shrikant S Tangade 2*
Abstract: In Wavelength Division Multiplexing (WDM) the method used to build a light-path connection from a source node to a
destination node is called Routing technique. An optical signal quality decreases as it travel through the network due to the physical
layer impairments. The light path in wavelength division multiplexed optical networks establishes a connection from source to the
destination node by carrying out electronic transition in between the nodes. The primary goal of Routing and Wavelength Assignment
(RWA) problem is to increase the number of calls or connection links efficiently by selecting the best route from the available routes.
Routing and Wavelength Assignment is a challenging topic in WDM optical networks even we have many algorithms available for
minimizing the blocking probability. Here in our work we are providing a literature survey on Routing and Wavelength Assignment
techniques in WDM networks and Finally, we will develop a new Routing and Wavelength Assignment algorithm that is going to
improve the performance in the network and reduces the Blocking Probability in WDM optical networks.
Asian Journal of Engineering and Technology Innovation
Volume 4, Issue 7
Published on: 7/05/2016
Cite this article as: Shashma M, Shrikant S Tangade. Survey on Different Routing and Wavelength Assignment Techniques in WDM
Optical Networks. Asian Journal of Engineering and Technology Innovation, Vol 4(7): 76-79, 2016.
INTRODUCTION
There is becoming a new growth in internet data due to
increase in bandwidth intensive applications such as Internet of
Things (IoT),Cloud Computing, Big Data. For its increasing
transmission capabilities, low signal attenuation and less Bit
Error Rate (BER) fiber has become a instinctive choice of
transmission for supporting rapid requirement of large data
transmission and reception and for fast processing [5].
In WDM many data signals modulate optical signals at
different wavelengths and out coming signals are integrated
and are transmitted at the same time over the single optical
fiber. In WDM every communication channel is allocated to a
different wavelength and multiplexed onto a single fiber. At the
destination wavelengths are spatially separated to different
receiver locations. These Optical networks capable of providing
required bandwidth. In a WDM network, all users
communicate with one another through WDM channels,
which are called as light-paths. A light-path should take the
same wavelength over all the fiber links through which it spans.
Advantages of Optical Networks
1. Optical Networks have the following Advantages [9]
2. Capacity of the fiber is high Restoration can be done
3. Can achieve long distance transmission Large Bandwidth
4. Less Weight, Small Diameter Attenuation is less
5. Signal distortion is less Power requirement is less
Wavelength reuse
6. Requires less space Cost effective
7. Reliable and Secure Flexible in nature
Figure 1: Wavelength Division Multiplexing
Reva Institute of Technology and Management, Rukmini Knowledge
Park, Kattigenahalli, Yelahanka, Near Border Security Bustop,
Bengaluru, Karnataka-560064, India.
Routing and Wavelength Assignment
A Method of identifying a route and relegating a wavelength to
the light-path is often referred as Routing and Wavelength
Assignment problem. The goal of this problem is to find a
route and relegate a wavelengths in such a manner, that should
reduce the utilization of network resources, while in the
meantime guaranteeing that two light-paths should not offer
1
Indian Institute of Science, C V Raman Ave, Bengaluru, Karnataka
560012, India.
E-mail: [email protected]
*Corresponding author
2
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Research Article
first shortest path, secondary is next shortest path and so on. If
two paths have same distance then any one path is chosen
randomly for connection establishment [1].
the same wavelength on same route. The optimum formulation
of the Routing and wavelength assignment is known as NPcomplete; in this way, heuristic arrangements are regularly
utilized. Usually There are three types of connection requests.
They are dynamic, static and incremental. In static connection
type the traffic is known in advance and then the connection
should establish for the traffic in such a way that should
minimize the use of resources In the network such as
wavelengths or fibers. in incremental type of traffic connection
request arrive successively and should built up a light-path and
this will stay for long time in the network. In dynamic type we
need to set up a connection after arrival of request and after
some amount of time the connection should be disconnected.
The main goal behind incremental and dynamic traffic cases is
to reduce the blocking of calls and to minimize the utilization
of network resources. In both the traffic cases we will consider
routing and wavelength assignment as two separate problems
in order to achieve more efficiency in solving the problem. [6]
Figure 3: Fixed Alternate Path Routing
In Figure 3 a solid line indicates a prime path and a dotted
line indicates the alternate path from node 0 to 2.
Adaptive Routing Based on Global Information
By making use of network state data this methodologies
improve the probability of building up a connection.
Centralized Versus Distributed Routing: Adaptive routing
adaptive routing might be implemented in either a centralized
or distributed manner by making use of global network
information. In a calculation, a centralized scheme single
element, for example, a network administrator, records or
holds complete system state data, and is responsible of
discovering routes and establishing light-paths for connection
demands. Because a centralized element handles the whole
system, there no need of a high level of coordination in
between the nodes; but in some cases the centralized entity may
become fail. Besides, a centralized scheme does not perform
well because it would need to keep up an extensive database to
deal with all nodes, connections, and links in the system.
Alternate Path Routing: By using global information, this is
another method for adaptive routing. It depends on set of
predefined paths between the nodes. After arrival of a
connection demand, an individual path is selected from the set
of predefined paths, and then a light-path is build up on that
path. The measures taking into account for path choice is
commonly, either a distance of the path or blockage of path.
Based on path lengths we have shortest path algorithm for
routing. In this first the connection establishment is done on
first shortest path, then the next shortest path and so on.
Unconstrained Routing: Based on global data the other type
of adaptive routing method is unconstrained routing that will
take all feasible routes between two nodes. By knowing the
present state of the network, that is what are the available
wavelengths an optimum path has to be selected by assigning a
cost to every link in the network. Based on the cost a minimum
cost route has to be selected for routing. After each connection
set up or detachment the present state of the network has to be
updated. There are two types of unconstrained routing namely
link-state and distance vector routing. In link-state routing
method each node has to maintain a record of network state
Fixed Routing
n fixed routing, for every source to destination node, an
individual route is determined. The net-work try to build a
connection between the pair of nodes by using earlier
determined fixed route. By doing so if common wavelength is
not found on each link, then the connection establishment will
not be done and the call has been blocked. This routing is easy
to design so exceptionally constrained for routing choices and
might lead to large scale of blocking.
Figure 2: Fixed Shortest Path Routing
Fixed
Alternate Routing: In this every node in the network has to
keep up a routing table that contains a number of various paths
from each source to destination node. In this we should also
main first shortest path, second shortest and so on. A prime
path is considered as first route between a pair of nodes in the
routing table based on shortest distance. Next the second route
is listed in the routing table that should not share any links
with the first route. Then the network try to make a connection
set up between a pair of nodes from these listed set of routes in
order with available wavelength after arrival of a request. If it is
not possible to build a connection from these listed routes then
that connection request is blocked and lost. In routing table the
routes are ordered based on distance so primary route is the
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Research Article
the heuristic with an optimum algorithm. A present regenerator placement strategy is used superior to the network
operation, to determine the nodes having regeneration
capability. They have used an A* best first search algorithm for
identifying the IA-RWA solution. This algorithm chooses a
path (from a set of pre-determined paths) by using least
Possible number of regenerators for every pair nodes. They
have constructed a search tree for identifying a possible path
for any connection request for any source to any destination
node. Pre-determined k shortest paths between each node pair
(within optical reach) helps the algorithm to reach the
destination rapidly. In this they have not carried out the
problem of managing the fault in the network.
In [5], the New routing and wavelength assignment strategy
for all optical networks without use of wavelength converters is
proposed. Simulations were accomplished on NSFnet optical
network. In this proposed weight function, few shortest paths
are determined for each source and destination by Dijsktras
modified algorithm. In this For connection request, the weight
is calculated for each route and route with maximum weight is
selected. Then they have compared blocking probabilities of
existing techniques with first fit approach for different number
of wavelengths for varied load conditions.In order to improve
further the network performance this can also be extended
with partial and sparse partial wavelength converters.
In [7], dynamic RWA scheme is proposed. In this they have
used adaptive routing for selecting the route and first-fit
approach for wavelength assignment. In order to set up a path
between a pair of nodes, first they will determine the delay and
bandwidth required on each link. The path which is congested
is not considering and the path which is less loaded and having
free wavelengths is chosen for path establishment. After that by
allocating minimum granularity values calculating the shortest
and low traffic path. Finally for alternate path selection RMSA
with HSMR algorithm is used.
In [4], the proposed algorithm for routing and wavelength
assignment first checks for quality of the light-path and if path
have acceptable quality then by finding the Q-factor of that
path they will select that path for connection establishment.
In [6], they have given brief explanation about the different
type of methods for routing and wavelength assignment for
optical networks and finally they have proposed Distributed
Relative Capacity Loss method that is well applied for a
distributed network and the routing scheme used is adaptive
technique.
information. In a distributed way each node determines a path
for connection set up. Then all nodes has to be communicated
if there is any changes in the state of the network. Therefore the
path set up or release will results in informing about the state of
the network to all the nodes. This will results in control
overhead. Next it will results in improper routing selection
based on the availability of outdated data. With global data the
distance-vector approach is also can be used. In this no need to
record the state of the network but rather every node should
have a table that have information about the wavelength and
distance on each link [1].
Figure 4: Adaptive Routing
Wavelength Assignment Techniques
We outline the wavelength - assignment approaches as follows.
1. Random Wavelength Assignment (R): In order to determine
all the available wavelengths on the necessary route this scheme
primly searches the wavelength space. A route is selected at
random based on wavelength availability.
2. First-Fit (FF): In this approach, all wavelengths are
numbered. A least numbered wavelength is taken instead of a
higher-numbered wavelength when searching a wavelength
space. Then the first available wavelength is selected. This
approach does not require any global information. The
computational cost of this approach is lower than the random
assignment scheme because each route does not required
searching of entire wavelength space.
3. Least-Used (LU): In this wavelength is selected which is
used least in the network. After that it will try to manage the
load in between the wavelengths. This approach finishes fastly
assignment of Long wavelength for routes. Thus the traffic that
travels through less number of hops is serviced in the network.
Compare to random performance is less and also gives more
communication overhead that is global data is needed
for
computing the least used wavelength. This is also needed extra
storage and computational cost hence practically this is not
useful. Most-Used (MU): This is inverse of least used and
this will selects the wavelengths which is used mostly. This
overcomes the problem of LU considerably. Storage, cost of
computation and communication overhead is same as that of
LU. This overcomes some of the problems of FF by computing
routes by using less number of wavelengths [6].
CONCLUSION
Due to emerging demand for higher bandwidth we are looking
for WDM optical networks because of their high capacity and
higher bandwidth and long distance transmission. These
WDM optical networks carrying high data so if there is any
LITERATURE SURVEY
In [2], they have proposed a heuristic algorithm for assigning a
dynamic light-path in translucent networks and have analyzed
78
Research Article
8.
failure in the link carrying the data then the data is going to lost
so setting up a alternate route in case of failure has became a
severe challenge now a days. Therefore in our work we have
given overview of some of the routing and wavelength
assignment techniques which have been used for reducing the
probability of blocking of connection set up in the network.
9.
10.
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